Plus it still seems highly unlikely. How do you prevent terrorism on a Space Elevator? And how many hundreds of miles around it would have to be unhabitable? (imagining the workmen dropping a wrench...."Heads!!")

Plus it still seems highly unlikely. How do you prevent terrorism on a Space Elevator? And how many hundreds of miles around it would have to be unhabitable? (imagining the workmen dropping a wrench...."Heads!!")

Plus this probably should go in a different discussion forum....

- binarysunrise

If we base our exploration of space on whether terrorism is a factor we may as well hand in our notice right now.

I seriously doubt that a terrorist attack on a viable space elevator design. It made some interesting reading in Robinsons fictional Mars books but his space elevator concept will most likely never leave the pages of fiction.

Terrorists knocking out one of the ribbon elevators wouldn't do much damage to anything other than the ribbon itself I would imagine and whatever was on it at the time. It'd be like a ticker tape parade or worrying about such a parade by claiming the ticker tape falling down is like dropping a tree from a skyscraper.

As for something falling off the ribbon (sorry no guys with wrenches for this construction project) the current design that is being worked on would have it's anchor point on the equator out in the Pacific Ocean, far from just about everything.

If we base our exploration of space on whether terrorism is a factor we may as well hand in our notice right now.

Agreed. We would never get anywhere. The best thing to do is just push through. Things can be built to try to eliminate the possibility of a terrorist attack, but it would take extra time and money. I say just worry about building it first and about guarding it once we find out if it really works or not

(To those unfamiliar with space elevators)
Don't forget these newer space elevators concepts are simply a massive super-sizing of a simple children's toy -- a ball tied to a rope. Space elevators are NOT Earth-standing structures. Nothing needs to hold up the elevator -- it's swung taut simply by the spinning earth

Common children's toy -- a ball tied to a rope. Swing it around, and you've demonstrated how the space elevator stays taut. The rotating Earth keeps the line stretched. As long as there's enough weight above the geostationary orbit, the centripetal force OVERCOMES gravity!

You do have to concede that the space elevator is more realistic now with the carbon nanotube "ribbon" concept. There's a lot of staggering engineering obstacles.

The excitement over one, would probably be similiar to the excitement from the 1858 transatlantic telegraph cable. (The 1866 cables were far more successful, though). Thousands of tons of continuous cable, all had to be rolled out flawlessly from a ship, without the cable breaking. These cables were extremely heavy (old thick impure copper, thick tar and early rubber-like substances called "gutta percha"; which was also used for 19th century golf balls as well). The 1857 attempt to roll the cable caused repeated snaps. Imagine several miles of cable pulling down on the ship, hanging diagonally, before it hit the ocean floor. Although underwater, you have to keep in mind that these cables were mostly metal and heavy tar-like substances, which meant immense amount of weight suspended as the cable-laying ship went across the Atlantic. These cables had to be among the strongest cables about 150 years ago, just because several miles

Today. Now we have cables that you can buy at stores (Home Depot, Walmart), that that can hang by its own weight by hundreds or thousands of miles hanging with enough room leftover to lift a small capsule. But that's not long enough for a space elevator. You can already use Home Depot nylon-like rope for a space elevator on many small bodies (i.e. for going into orbit around asteroids), it's strong enough. Today, household cable can be suspended by hundreds of miles -- the yellow cable you buy from Walmart or Home Depot (of course, you'd need weatherproofing and take into factor of water absorption, and other Murphy's Law factors). These cables are so light, that it's only a few pounds per mile (only a kilograms per kilometer) and you've seen some of those hold up the weight of a car (thousands of kilograms or thousands of pounds). A Discovery show showed some similiar cable holding up a whopping 5 cars. So these cables can easily be suspended in the 3-figure range (and the stronger cables, likely developed for the military, in the low 1000's range - the 4-figure range!), if you had something that high-up to suspend from. (Too bad the geostationary orbit isn't only 1000 kilometers above the surface of Earth!)

It's like a rope tied to a ball -- the rotating of the planet or body "swings" the counterweight away from the body. All you need is a big enough counterweight above the geostationary orbit, so that you've got "pull" that exceeds gravity, simply caused by the spin of the planetary body (i.e. Earth).

A space elevator would be very easy on an asteroid surface because asteriods are low gravity, and we even already have rope that can make a moon elevator already. But it's fiendishly difficult for Planet Earth -- it's only recently that the 'unobtainium' was found (Carbon nanotubes!) that just suddenly made space elevators very possible.

NOW....A pratical space elevator, requires 5-figures worth of cable or ribbon, something like 60,000 kilometers. Ignore past space elevator concepts like those found in books and in the 1980's and before which was tall structures or similiar, these concepts are unrealistic.

HOWEVER, the cable/ribbon concept is far more realistic -- the mere spinning of planet Earth swings the cable outwards. (All you need to do is enough counterweight ABOVE the geostationary orbit. Counterweight above geostationary can be anything, such as simply extra cable, and/or junked climbers, etc. Satellite orbit slower above the geo orbit, but if you try to move that satellite to follow planet Earth rotation speed, that object wants to "pull away" (centripetal force). See? It's now easy to understand centripetal force.

See, space elevators are simple physics -- the physics are simpler to learn than rocket science! (Although learning how to make carbon nanotubes is arguably a LOT more complex than rocket science And of course, designing a climber that crawls up a cable. And of course, powering the climber.)

The other problems may prevent the space elevator from going up, but you do have to concede that it's a hell lot more realistic now.

did you read Edwards' documents on the NIAC homepage? He has worked out that the counterweight doesn't need to be an asteroid. The cable is coming down from slightly aboce geostationary orbit and then linked to earth. Edwards proposes first to send several torso-like elevators up to geostationary orbit that together have the required mass to form a sifficient counterweight.

The documents are around two years old now - he might have worked out that very more detailed in between.

What I'm missing a little bit is search for synergies between all the concepts on that site. There are several concepts using cables and tethers - they all might get advantages from one another. Who might do this search one day? A private enterpreneur? Someone like Burt Rutan? May be.

Oh yes, suspension bridges. Miles and miles of cables under immense tension -- the physics of a suspension bridge is actually surprisingly more complex than a space elevator. However, it's very good reading.

Amazing fact for new users: All 60,000 kilometers space elevator would weigh less than ONE 1-kilometer-long suspension bridge primary cable (the one that curves between the towers).

In fact, 60,000 kilometers of Walmart-purchased yellow plastic rope would weigh less too, but that stuff isn't strong enough for a space elevator except from the surface of small moons and large asteroids.

According to one estimate I read somewhere, only approximately 24 tons of material is needed for a test/starter space elevator ribbon (a small one for light objects). Once fully built, a space elevator is only a few kilograms per kilometer; that's how lightweight carbon nanotubes are.

I am aware -- the most recent documents I have read is to junk the construction climbers above the geostationary orbit, to be used as counterweight to help keep the space elevator taut by centripetal force. (the proverbial ball at the end of a rope). Not many tons of material appears to be needed and you can launch objects beyond Planet Earth just by letting go of the space elevator at the far end significantly above the geostationary orbit. I have made minor edits to my post to clarify the asteroid confusion;

Some of the stuff I read. Good reasoning. I think many things can be overcome, but I think these will probably be the biggest engineering challenges. About challenges. In fact, terrorism isn't even the biggest challenge as there are ways to protect it and even if that happens, it will be no more dangerous than a falling Skylab when collapsing, anyway, mostly due to the newspaper-style-flutter of falling lightweight nanutube ribbon (unlike the disaster scenario found in some scifi novels). It'll get rebuilt anyway. Even powering the climbers isn't even the biggest challenge in my opinion, and space debris resistance is pretty good in a ribbon, and multiple redundant ribbons can be used in the same location, and the elevator can be swung a kilometer to the left or right like swinging a rope (i.e. by moving the ocean platform that anchors the bottom)

I see no problem at least hanging an initial ribbon sometime this century (perhaps in a couple of decades from now), but now to give at least be a little devil's advocate as well, I still have some doubts about the ability to make such pure carbon nanotube material that is 60,000 kilometers long AND resists the wear-and-tear of mechanical climbers climbing up the rope. All the other stuff can be overcome, but once the elevator is in operation, it's not going to last long with climbers, especially if one breaks down or "slips" a little bit, damaging the ribbon slightly. A critical point of failure will occur (a weak link in the chain, so to speak). I think that longevity issues will be a major problem in wear-and-tear. There isn't that much safety margin in carbon nanotubes when this factor is taken into account. I think that durability is going to be a major problem for a ribbon that only weighs a few kilograms a kilometer, even though carbon provides some of the strongest material avaialble. Atomic oxygen is going to hurt it a lot, perhaps the radiation belts will degrade it, and the weather in the atmosphere. And getting rid of electricity from the ribbon, because it acts as a gigantic antenna, especially as it shakes, swings, and flutters a little bit through Earth's magentic field, generating electricity that flows inside the carbon nanotubes. The environment will be hell on lightweight space elevator ribbon, and lifetime of a ribbon could be pretty short, requiring the ribbon to be constantly rebuilt. Undetected weak spots in the ribbon. Needing to monitor damage to the ribbon without sending a climber onto it to inspect it. I'd envision at least one or two disasters caused by a snapping space elevator ribbon, but apart from less than 5 tons of rubberlike snapback slamming the offshore platform (may significantly slowed down by air friction, so it may end up being a flutter landing on the offshore platform), with the rest of the ribbon above the atmosphere burning up in the atmosphere as it accelerates by gravity uninibited and hits the top of the atmosphere, and a falling climber possibly lost into orbit, or hitting Earth like a falling satellite, it would be pretty much purely a financial disaster (due to cost of the space elevator). But more would get built eventually once we got the guts to do it again, maybe decades later, maybe right away. Just as early airplanes were rebuilt after the first airplane crashes (Or in the case of the transatlantic telegraph, the 1866 transatlantic telegraph cable after the 1858 one failed after just 2 months.).

Without further information, if I had to make any bet what will be one of the more difficult items to overcome, someone is going to need to figure out how to resist electricity generation (moving wire in the prescence of magnetic field -- moving space elevator in the prescence of Earth's magnetic field -- generates electricity). If I remember right, one space shuttle tether experiment ended because of a big electric spark at one end of the tether broke the tether, which shows that this can be a major problem. And carbon nanutobes conduct electricity better than copper! An electricity station at the bottom of the space elevator might help, to treat the ribbon as an electric generator, but what about electricity generated over 30,000 kilometers above the surface?; even the ribbon isn't that good a conductor to get rid of built-up electricity that far away. It could burn up with electricity generated if the ribbon accidentally moves too much, especially if too much electricity moves across one single point on the ribbon. It took only a short space tether to damage itself from captured electricity in a space tether experiment a few years ago that I read about, so that's where my concerns about this comes from... This has already been discussed by the space elevator people to some extent, but I am wondering how much this problem can be solved.

In stead of a space elevator that goes all the way down to earth, we could build already now, a space elevator that starts in LEO and goes up beyond GEO. The difference is that in stead of strength of nanotubes and required nanotechnology, a rigid structure is needed to bring up payloads from LEO to whatever orbit or beyond. In stead of nanotubes a relatively small and light steel rail would do the job. The whole stuff could be powered by solar cells (for powering the maglev) and some small thrusters could keep the thing in place.

Could be started now. Each Shuttle can bring approximatively 50 km of rail in orbit. (Maybe even far more, depends on how rigid the structure needs to be) Something like 750 shuttle flights or 175 Energya (shuttle-c ?) flights needed. Alternatively this structure can be build on the moon and catapulted into space.

In the extreme case where rigidness is not required, the whole job could be done with just 40000 km of cable brought into space and some additional solar cells and other equipment. Just a few shuttle flights ?

In stead of a space elevator that goes all the way down to earth, we could build already now, a space elevator that starts in LEO and goes up beyond GEO.

It's a valid idea. Only one hitch: it basically dispenses with the entire reason for having an elevator in the first place. Getting from one orbit to another is pretty cheap, as far as fuel's concerned: all you have to do is keep accelerating just the tiniest bit, and you'll keep climbing. Getting to orbit from the surface isn't.

In stead of a space elevator that goes all the way down to earth, we could build already now, a space elevator that starts in LEO and goes up beyond GEO.

It's a valid idea. Only one hitch: it basically dispenses with the entire reason for having an elevator in the first place. Getting from one orbit to another is pretty cheap, as far as fuel's concerned: all you have to do is keep accelerating just the tiniest bit, and you'll keep climbing. Getting to orbit from the surface isn't.

Yes, if you keep thing limited to orbits.... but the point is that the maglev of this elevator can bring whatever payload also from LEO to escape velocity and that is far from a "tiniest bit".
See the picture ?